EMI is typically generated by digital signals. This includes pulse width modulation (“PWM”), which emits “noise” that can adversely affect other electronic equipment operating in the vicinity. RF noise is particularly troublesome when it is emitting in an MRI scan room. One single digital signal can “spray” harmonics of the fundamental frequency and emit a full spectrum of RF, both conducted and radiated. This spectrum, ranging from low kilohertz (“kHz”) to gigahertz (“GHz”) can generate artifacts in the MRI scan image, which is highly undesirable. The artifacts that are generated can seriously impair the quality of the imaging results. Accordingly, it is desirable to avoid generating artifacts within such imaging rooms, including those generated by LED lighting and related controls.
A typical MRI scan room has a pass-through RF filter for each LED light (or “lumenaire”) or one RF filter per lighting zone of luminaires. These RF filters require wall space, can be expensive, and limit the flexibility of the MRI lighting system. To save money, a designer might wire all luminaires in parallel and use one large RF filter. One large RF filter is expensive. Such a configuration has other drawbacks as well. For example, if direct current (“DC”) luminaires are employed, this requires a bus voltage and this is not optimal for LED lighting. A single DC bus voltage is susceptible to voltage drops on the line as the number of luminaires, and distance between them, is increased. This condition could result in luminares with varying light levels or too much LED drive current. This could also limit the possible lighting zones of the system to one. If AC is used, the luminaire must have an LED driver in the scan room, which would likewise cause EMI while also increasing cost. If the designer wants multiple zones, with a bus voltage, then a RF filter is required for each zone. All of the drawbacks mentioned above still exist, with the multiple zone configuration, and now there will be an additional filter for each lighting zone, thereby further increasing system size and cost.